Transmission apparatus and control signal mapping method

ABSTRACT

Disclosed is a transmission apparatus which enables high transmission-rate communication by mapping DMRSs in a way adapted to the reception environment of each terminal. The transmission apparatus includes: reference signal configuration section ( 101 ) that configures a DMRS mapping pattern for each terminal and outputs a DMRS and information indicating the DMRS mapping pattern; and transmission section ( 106 ) that transmits a transmission signal including the information indicating the DMRS mapping pattern configured by reference signal configuration section ( 101 ) and the DMRS mapped according to the DMRS mapping pattern to the terminal.

TECHNICAL FIELD

The present invention relates to a transmission apparatus and a controlsignal mapping method.

BACKGROUND ART

In recent years, transmitting not only speech data but also large volumedata such as still image data and moving image data has become commonalong with the increasing adoption of multimedia-enabled information incellular mobile communication systems. Meanwhile, studies have beenactively carried out to achieve high transmission-rate communicationusing a wide radio band, multiple-input multiple-output (MIMO)transmission technology, and interference control technique in long termevolution advanced (LTE-Advanced).

In addition, studies have been carried out on achieving a hightransmission rate at hotspots through deployment of small cells, eachbeing a radio communication base station apparatus (hereinafter,abbreviated as “base station”) using low transmission power in cellularmobile communication systems. Allocating a frequency different from thatfor macro cells as a carrier frequency for operating small cells hasbeen also under study. A high frequency such as 3.5 GHz has become acandidate. When small cells and macro cells are operated using differentfrequencies, transmission signals from macro cells do not interfere withcommunication performed by small cells. Accordingly, the deployment ofsmall cells can achieve high transmission-rate communication.

In LTE-Advanced, a cell-specific reference signal (CRS) or ademodulation reference signal (DMRS) is used as a reference signal (RS)used for demodulating a physical downlink shared channel (PDSCH), whichcorresponds to a data signal.

CRSs are also used for channel quality measurement in addition todemodulation of data signals while the number of antenna ports and theresource positions for CRSs are determined on a per cell basis. For thisreason, it is difficult to change the amount of resources for the CRSsfor each radio communication terminal apparatus (hereinafter,abbreviated as “terminal,” which may be also called a user equipment(UE)).

Meanwhile, the number of antenna ports and the resource positions forDMRSs are determined on a per user basis, and DMRSs are mainly used fordemodulating data signals. In addition, DMRSs mapped in resource block(RB) pairs for a different terminal (to be described, hereinafter) haveno effect on signal assignment. For this reason, it is easier tooptimize the amount of resources for DMRSs for each terminal.

Small cells provide coverage for low-mobility terminals and indoorterminals with a small delay spread, supposedly. The channel quality ofthese terminals is expected to be good. In this respect, studies havebeen carried out on further increasing the transmission rate throughDMRS reduction for terminals having good channel quality and use of theresources that have become available as a result of reducing DMRSs, as adata region (see, Non-Patent Literatures (hereinafter, referred to as“NPL”) 1 and 2).

(Explanation of Resources)

In LTE and LTE-Advanced, one RB consists of 12 subcarriers in thefrequency-domain and 0.5 msec in the time-domain. A resource unit formedby combining two RBs in the time-domain is called an RB pair.Accordingly, an RB pair consists of 12 subcarriers and 1 mesc. An RBpair may be simply called an RB when the term is used for representing agroup of 12 subcarriers in the frequency domain. In addition, an RB pairis called a physical RB (PRB) in the physical layer. Moreover, thefirst-half RB (0.5 msec) of a PRB pair is called a first slot, and thesecond-half RB (0.5 msec) of the PRB pair is called a second slot.

In addition, a unit consisting of one subcarrier and one OFDM symbol iscalled a resource element (RE). The number of OFDM symbols per RB pairvaries depending on the CP length of OFDM symbols. In the case of normalCP, each RB pair includes 14 OFDM symbols. In the case of extended CP,each RB pair includes 12 OFDM symbols.

FIG. 1 illustrates a DMRS mapping pattern in the case of normal CP. Whenonly antenna ports #7 and #8 are used, only 12 REs are allocated toDMRSs. When antenna port #9 is used at least, 24 REs are allocated toDMRSs. When antenna ports #7, #8, #9 and #10 are used, antenna ports #7and #8 are CDMA multiplexed by means of orthogonal cover codes (OCCs) onthe adjacent OFDM symbols of the same subcarrier and antenna ports #9and #10 are CDMA multiplexed by means of OCCs on the adjacent OFDMsymbols of the same subcarrier. Moreover, when antenna ports #11, #12,#13, and #14 are used, antenna ports #7, #8, #11, and #13 are CDMAmultiplexed by means of orthogonal cover codes using four REs of thesame subcarrier and antenna ports #9, #10, #12, and #14 are CDMAmultiplexed by means of OCCs using four REs of the same subcarriers.

Multiple antenna ports are used in single user MIMO (SU-MIMO) and multiuser MIMO (MU-MIMO). In SU-MIMO, antenna ports #7 to #14 can be used fora single terminal. However, only antenna ports #7 and #8 can be eachused as a single antenna port, and for the number of antenna ports X(>1), antenna ports #7, #8, . . . #(X+6) are used. For example, when thenumber of antenna ports is 6, antenna ports #7, #8, #9, #10, #11, and#12 are used. MU-MIMO based on orthogonal multiplexing is achieved bymultiplexing antenna ports #7 and #8 by means of OCCs. However, eachterminal is only aware of allocation for the terminal and thus cannotknow whether or not MU-MIMO is actually performed.

(Reduction in Frequency-Domain Direction)

FIGS. 2A and 2B illustrate an example of a DMRS mapping pattern in whichDMRSs are reduced in the frequency-domain direction. Assigning thismapping pattern to a terminal in a reception environment where thechange in channel quality in the frequency-domain is moderate, such asan environment where a terminal is located indoors and with a smalldelay spread can minimize the degradation of reception quality due tothe reduction of DMRSs. For reducing DMRSs in the frequency-domaindirection, multiplexing is performed using four REs of the samesubcarriers. Thus, CDMA multiplexing of antenna ports #7, #8, #11, and#13 and CDMA multiplexing of antenna ports #9, #10, #12, and #14 can besupported.

(Reduction in Time-Domain Direction)

FIG. 3 illustrates an example of a DMRS mapping pattern in which DMRSsare reduced in the time-domain direction. Assigning this mapping patternto a low-mobility terminal in a reception environment where the changein channel quality in the time-domain is moderate can minimize thedegradation of reception quality due to the reduction of DMRSs. However,when antenna ports #7 to #14 are used, antenna ports #7, #8, #11, and#13 are to be CDMA multiplexed using four REs of the same subcarrier,and antenna ports #9, #10, #12, and #14 are to be CDMA multiplexed usingfour REs of the same subcarrier. Accordingly, antenna ports #11 to #14cannot be supported by the current design.

CITATION LIST Non-Patent Literatures

NPL 1

-   R1-130022 “Analysis and initial evaluation results for overhead    reduction and control signaling enhancements”    NPL 2-   R1-130138 “Downlink DMRS reduction for small cell”

SUMMARY OF INVENTION Technical Problem

In operation where a terminal changes a connection-destination smallcell every subframe, the reception quality also changes every smallcell. Accordingly, the optimum DMRS pattern also changes every subframe.

However, the DMRS mapping method of the related art assumes that a fixedpattern is used to map DMRSs for all terminals. Accordingly, the methodis not adapted to the reception environment that varies every terminal.

In addition, even if a certain base station attempts to increase thechannel quality by increasing the DMRS power (power boosting) in thecase where the same pattern is used to map DMRSs for a plurality ofneighboring cells, it is difficult to increase the channel qualitybecause the amount of interference increases when a base station forminganother cell increases the DMRS power on the same resources.

It is an object of the present invention to provide a transmissionapparatus and a control signal mapping method each of which enables hightransmission-rate communication by mapping DMRSs in a way adapted to thereception environment of each terminal.

Solution to Problem

A transmission apparatus according to an aspect of the present inventionincludes: a reference signal configuration section that configures ademodulation reference signal (DMRS) mapping pattern for each receptionapparatus; and a transmission section that transmits a transmissionsignal including information indicating the DMRS mapping pattern, and aDMRS mapped in a resource according to the DMRS mapping pattern.

A control signal mapping method according to an aspect of the presentinvention includes: configuring a demodulation reference signal (DMRS)mapping pattern for each reception apparatus; and transmitting atransmission signal including information indicating the DMRS mappingpattern and a DMRS mapped in a resource according to the DMRS mappingpattern.

Advantageous Effects of Invention

According to the present invention, a DMRS mapping pattern can beconfigured for each terminal, which makes it possible to map DMRSs in away adapted to the reception environment of each terminal and thus toenable high transmission-rate communication.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an example of how DMRSs are mapped;

FIGS. 2A and 2B are diagrams illustrating an example of a mappingpattern in which DMRSs are reduced in the frequency-domain direction;

FIG. 3 is a diagram illustrating an example of a mapping direction;

FIGS. 4A to 4D are diagrams illustrating DMRS mapping patterns andsignaling in the case of normal CP and DL subframes, according toEmbodiment 1 of the present invention;

FIGS. 5A and 5B are diagrams illustrating DMRS mapping patterns andsignaling in the case of extended CP and DL subframes, according toEmbodiment 1 of the present invention;

FIGS. 6A to 6C are diagrams each illustrating a DMRS mapping patterncorresponding to a bit sequence in which all the bit values are zero,according to Embodiment 1 of the present invention;

FIG. 7 is a block diagram illustrating a primary configuration of a basestation according to Embodiment 1 of the present invention;

FIG. 8 is a block diagram illustrating a primary configuration of aterminal according to Embodiment 1 of the present invention;

FIG. 9 is a block diagram illustrating a configuration of the basestation according to Embodiment 1 of the present invention;

FIG. 10 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present invention;

FIGS. 11A and 11B are diagrams illustrating an example of a DMRS mappingpattern in a variation of Embodiment 1 of the present invention;

FIGS. 12A and 12B are diagrams illustrating another example of the DMRSmapping pattern in the variation of Embodiment 1 of the presentinvention;

FIG. 13 is a diagram illustrating an example of a DMRS mapping patternaccording to Embodiment 2 of the present invention;

FIGS. 14A and 14B are diagrams illustrating an example of a DMRS mappingpattern according to additional embodiment 1 of the present invention;

FIG. 15 is a diagram illustrating an example of a DMRS mapping patternaccording to additional embodiment 2 of the present invention;

FIGS. 16A and 16B are diagrams illustrating an example of a DMRS mappingpattern according to additional embodiment 3 of the present invention;

FIGS. 17A to 17C are diagrams illustrating examples of a DMRS mappingpattern according to additional embodiment 4 of the present invention;and

FIGS. 18A to 18C are diagrams illustrating examples of a DMRS mappingpattern according to additional embodiment 5 of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be notedthat, the term “DMRS mapping pattern” used in the following descriptionincludes both of a pattern in which DMRSs are mapped in all ofpredetermined REs in each of which a DMRS can be mapped (hereinafter,referred to as “DMRS-mappable RE”) and a pattern in which DMRSs arereduced by not mapping DMRSs in some of the predetermined DMRS-mappableREs according to a predetermined rule.

(Embodiment 1)

(Summary) In Embodiment 1, a DMRS mapping pattern is indicated to eachterminal by signaling using multiple bits. Each of the bits used in thissignaling indicates whether or not to map and transmit DMRSs in acorresponding one of DMRS groups. Each of the DMRS groups is formed of aplurality of adjacent DMRS-mappable REs. When the number of DMRS antennaports is at least three (i.e., when antenna port #9 is used), a DMRSgroup includes four adjacent REs corresponding to two REs in thesubcarrier direction and two REs in the OFDM symbol direction. Inaddition, when the number of DMRS antenna ports is not greater than two,a DMRS group is configured to include two adjacent REs corresponding toone RE in the subcarrier direction and two REs in the OFDM symboldirection. Accordingly, a mapping pattern in which DMRSs are reduced inthe time-domain direction can be assigned to a low-mobility terminal,and a mapping pattern in which DMRSs are reduced in the frequency-domaindirection can be assigned to a terminal with a small delay spread.

(Normal CP)

FIGS. 4A to 4D are diagrams illustrating DMRS mapping patterns andsignaling in the case of normal CP and DL subframes. In the case ofnormal CP, the number of DMRS groups is set to six, and the DMRS groupsare indicated by A, B, C, D, E, and F, respectively. FIGS. 4A and 4Billustrate patterns used when the number of antenna ports is at leastthree, while FIGS. 4C and 4D illustrate patterns used when the number ofantenna ports is two or less. FIGS. 4A and 4C illustrate patterns inwhich no DMRS is reduced, while FIGS. 4B and 4D illustrate patterns inwhich DMRSs are reduced. In addition, each bit value “1” indicates thatDMRSs are mapped and transmitted in a corresponding one of the DMRSgroups, while each bit value “0” indicates that no DMRS is transmittedin a corresponding one of the DMRS groups. In the examples illustratedin FIGS. 4B and 4D, the bit sequence indicates “1,0,1,0,1,0,” so thatDMRSs are transmitted only in DMRS groups A, C, and E, while no DMRS istransmitted in DMRS groups B, D, and F. The terminal used in theseexamples performs channel estimation using the DMRSs in DMRS groups A,C, and E.

It should be noted that, the OFDM symbols on which DMRSs are mapped in aspecial subframe are different from those in a normal DL subframe, butcan be divided into six DMRS groups as in the case of DL subframes.

(Extended CP)

FIGS. 5A and 5B are diagrams illustrating DMRS mapping patterns andsignaling in the case of extended CP and DL subframes. In the case ofextended CP, only antenna ports #7 and #8 are used, and antenna port #9or any subsequent antenna ports are not used. In FIGS. 5A and 5B, thenumber of DMRS groups is set to eight, and the DMRS groups are indicatedby A, B, C, D, E, F, G, and H, respectively. FIG. 5A illustrates apattern in which no DMRS is reduced, while FIG. 5B illustrates a patternin which DMRSs are reduced. In the example illustrated in FIG. 5B, thebit sequence indicates “1,0,1,0,1,0,1,0,” so that DMRSs are transmittedonly in DMRS groups A, C, E, and G, while no DMRS is transmitted in DMRSgroups B, D, F, and H. The terminal used in this example performschannel estimation using the DMRSs in DMRS groups A, C, E, and G.

As described above, grouping two REs adjacent to each other in the OFDMsymbol direction on the same subcarrier, and switching between DMRStransmission and no DMRS transmission make it possible to keep CDMAmultiplexing for two antenna ports (#7 and #8, or #9 and #10) by meansof OCCs in the two REs in each group. In addition, grouping four REsincluding two REs on subcarriers adjacent to each other when antennaport #9 is used at least makes it possible to avoid multiplexing of datawith a DMRS when an RE not used for a DMRS is allocated to a PDSCH. Itshould be noted that, when a PDSCH and a DMRS of different antenna portsare multiplexed, the operation of a receiving-side interferencecanceller becomes complicated.

(Special Operation)

When a bit sequence in which all the bit values are equal to “0”(hereinafter, referred to as “all-0 bit sequence”) is defined as a bitsequence indicating not to transmit any DMRS group, the terminal cannotperform channel estimation and thus cannot demodulate a PDSCH in thiscase. For this reason, the all-0 bit sequence is defined as a bitsequence indicating a special operation. Examples of the specialoperation will be described, hereinafter.

Operation Example 1 New Carrier Type (NCT) in which Neither CRS norPDCCH is Mapped

In this example, the all-0 bit sequence is defined to indicate thatDMRSs are mapped on the top two OFDM symbols. FIG. 6A is a diagramillustrating an example of a DMRS mapping pattern of this operationexample.

In NCT, the operation is supposedly performed using a DMRS and anenhanced PDCCH (EPDCCH) to be demodulated using the DMRS, withoutmapping any CRS or PDCCH. LTE-Advanced is designed assuming that a DMRSis mapped in a subframe in which a CRS and a PDCCH to be demodulatedusing the CRS are mapped. Since a PDCCH is mapped on the top OFDM symbolof a subframe, a DMRS is mapped on an OFDM symbol other than the topOFDM symbol. In NCT in which no PDCCH is mapped, using the top OFDMsymbol for a PDSCH has been discussed.

However, when a PDSCH is mapped on the top OFDM symbol, the intervalbetween the PDSCH and a DMRS becomes large. As a result, there arises aconcern that channel estimation accuracy is degraded. For this reason,DMRSs are mapped on the top two OFDM symbols in this operation example.Accordingly, channel estimation accuracy can be improved for a terminalpredicted to have poor channel estimation accuracy.

Operation Example 2

In this operation example, the all-0 bit sequence is defined to indicatethat DMRSs are mapped in every other RB pair. FIG. 6B is a diagramillustrating an example of a DMRS mapping pattern of this operationexample. In this operation example, DRMSs are mapped only in even RBpairs and no DMRS is mapped on any odd RB pairs. Accordingly, the numberof REs in which DMRSs are mapped can be reduced to approximately half.

Operation Example 3

In this operation example, the all-0 bit sequence is defined to indicatethat a PDSCH is demodulated using a CRS. FIG. 6C is a diagramillustrating an example of a DMRS mapping pattern of this operationexample. In this operation example, no DMRS is mapped but CRSs aremapped, instead. This operation example is particularly effective for abackward compatible carrier type (BCT), which allows connection of allthe terminals compliant with releases 8 to 11. Since BCT includes asubframe in which CRSs are transmitted, when precoding for a PDSCH inthe subframe can be the same as that for the CRSs, all the REs that aresupposed to be used for DMRSs can be used for the PDSCH. Thus, thechannel estimation accuracy can be maintained even when DMRS reductionis performed.

(Method for Indicating DMRS Mapping Pattern)

Hereinafter, a description will be provided regarding a method forindicating a DMRS mapping pattern to a terminal from a base station inEmbodiment 1.

(Option 1: Combination of Higher Layer Signaling and DCI Indicating)

In option 1, a base station previously indicates DMRS mapping patterncandidates to a terminal via higher layer signaling, then dynamicallyselects one of the DMRS mapping pattern candidates and indicates theselected DMRS mapping pattern to the terminal via DCI transmitted on aPDCCH or EPDCCH.

As described above, this two-step indicating can reduce the number ofsignaling bits used for indicating by DCI. Moreover, dynamic signalingcan be performed in common with a PDSCH RE Mapping and Quasi-Co-Locationindicator (PQI) transmitted in DCI format 2D. Incidentally, PQI consistsof two bits and is information indicating a parameter set configured byhigher layers as illustrated in Table 1.

TABLE 1 Value of ‘PDSCH RE Mapping and Quasi-Co-Location Indicator’field Description ‘00’ Parameter set 1 configured by higher layers ‘01’Parameter set 2 configured by higher layers ‘10’ Parameter set 3configured by higher layers ‘11’ Parameter set 4 configured by higherlayers

Higher layers configure a maximum of four parameter sets. The parametersto be configured are as follows.

Number of CRS antenna ports for PDSCH RE mapping

CRS frequency shift for PDSCH RE mapping

MBSFN subframe configuration for PDSCH RE mapping

Zero-power CSI-RS resource configuration for PDSCH RE mapping

PDSCH starting position for PDSCH RE mapping

CSI-RS resource configuration identity for PDSCH RE mapping

In Option 1, “Reduced DMRS pattern” is added to the parameters.Accordingly, a DMRS mapping pattern can be indicated without anyincrease in the number of bits to be dynamically indicated using DCI.The parameters indicated by PQI are mainly used for specifying CoMPtransmission point parameters. Accordingly, it is possible to change aDMRS mapping pattern as well for each transmission point. Thus, eachbase station can select a DMRS mapping pattern in accordance with thechannel quality.

(Option 2: Indicating Via Higher Layer Signaling and (E)PDCCH Set Type)

In Option 2-1, a DMRS mapping pattern is configured for each EPDCCH set(or PDCCH set) via higher layer signaling. LTE-Advanced allows twoEPDCCH sets (search spaces) to be configured. Accordingly, a terminalchanges a DMRS mapping pattern in accordance with an EPDCCH set by whicha PDSCH is assigned. An EPDCCH set can set the number of RB pairs whilesetting localized allocation or distributed allocation for each set.

Thus, the reception quality of a terminal varies for each EPDCCH set.Accordingly, since each base station can select an EPDCCH set and PDCCHset in accordance with the change in the channel quality of a terminal,the base station can select a DMRS mapping pattern in accordance withthe channel quality.

In Option 2-2, a DMRS mapping pattern is configured for each candidateEPDCCH position via higher layer signaling. In LTE-Advanced, a pluralityof EPDCCH candidate positions is configured for each aggregation level.Each terminal blind-decodes the EPDCCH candidate positions and detects aDL grant and UL assignment. Accordingly, the terminal changes the DMRSmapping pattern in accordance with the position detected from the EPDCCHcandidate positions. Thus, since each base station can select an EPDCCHcandidate position in accordance with the change in the channel qualityof a terminal, the base station can select a DMRS mapping pattern inaccordance with the channel quality.

(Option 3: Selection of DMRS Mapping Pattern According to Allocated RBPairs)

Each terminal selects a DMRS mapping pattern according to the allocatedRB pairs. Thus, no DMRS mapping pattern has to be indicated by DCI, sothat the number of signaling bits can be reduced.

In Option 3-1, a DMRS mapping pattern is selected according to thenumber of allocated RB pairs. Each base station assigns a DMRS mappingpattern including a larger number of reduced DMRSs to a terminalallocated the number of RB pairs not less than N, and assigns a DMRSmapping pattern including a smaller number of reduced DMRSs to aterminal allocated the number of RB pairs less than N. The channelquality of a terminal allocated a larger number of RB pairs is good inmany cases, so that the base station can select the number of DMRSs tobe reduced, in accordance with the channel quality.

In Option 3-2, a DMRS mapping pattern is selected according to thesystem bandwidth. A precoding resource block group (PRG) size variesdepending on the system bandwidth. The term “PRG size” refers to a rangeof adjacent RB pairs to which the same precoding is supposedly applied.Accordingly, when the PRG size is equal to one, it is possible to assumethat different precoding is used for a DMRS in an adjacent RB pair.Thus, the DMRS in the adjacent RB pair cannot be used. In this case, thebase station assigns a DMRS mapping pattern including a smaller numberof reduced DMRSs. Meanwhile, when the PRG size is equal to two orgreater, it is possible to assume that the same precoding is used for anadjacent RB pair. In this case, the base station assigns a DMRS mappingpattern having a larger number of reduced DMRSs.

In Option 3-3, a DMRS mapping pattern is selected according to theallocated number of contiguous RB pairs. Each base station assigns aDMRS mapping pattern including a larger number of reduced DMRSs to aterminal allocated the number of contiguous RB pairs not less than M,and assigns a DMRS mapping pattern including a smaller number of reducedDMRSs to a terminal allocated the number of contiguous RB pairs lessthan M. The channel quality correlation between contiguously mapped RBpairs is predicted to be high, so that each terminal can perform channelestimation using a value obtained by interpolating DMRSs between the RBpairs. Accordingly, it is possible to minimize the degradation ofreception quality due to the DMRS reduction even when the number ofreduced DMRSs is increased in this case.

In Option 3-4, a DMRS mapping pattern is selected according to theallocated RB pair number or resource block group (RBG) number. Each basestation determines the DMRS mapping pattern according to the top RB pairnumber or RBG number of the allocated resources. The DMRS mappingpattern can be flexibly determined by changing the RB to be allocated tothe top of the allocation resources. When the number of patterns isrepresented by X, the pattern may be determined by modulo operation of Xand the RB pair or DMRS number.

It is to be noted that, Embodiment 1 has been described regarding thecase where the bit sequence that specifies a DMRS mapping pattern isindicated by higher layers, but Embodiment 1 is not limited to thiscase, and the bits included in DL DCI may be used for indicating as thebits specifying a DMRS mapping pattern. Accordingly, a plurality of DMRSmapping patterns can be dynamically selected.

(Configuration of Communication System)

A communication system according to Embodiment 1 includes a transmissionapparatus and a reception apparatus.

In particular, Embodiment 1 will be described with base station 100 asan example of the transmission apparatus and terminal 200 as an exampleof the reception apparatus. This communication system is an LTE-Advancedsystem, for example. In addition, base station 100 is a base stationcompliant with the LTE-Advanced system and terminal 200 is compliantwith the LTE-Advanced system, for example.

(Main Configuration of Base Station 100)

FIG. 7 is a block diagram illustrating a primary configuration of basestation 100 according to Embodiment 1.

In base station 100, reference signal configuration section 101generates DMRSs and configures a DMRS mapping pattern for each terminal200. In addition, reference signal configuration section 101 outputsDMRSs and information indicating the configured DMRS mapping pattern.

Transmission section 106 transmits a transmission signal including theinformation indicating the DMRS mapping pattern configured by referencesignal configuration section 101 and the DMRSs mapped according to theDMRS mapping pattern to terminal 200.

(Primary Configuration of Terminal 200)

FIG. 8 is a block diagram illustrating a primary configuration ofterminal 200 according to Embodiment 1.

In terminal 200, reference signal configuration section 206 configures aDMRS mapping pattern based on a control signal included in a receivedsignal. In addition, reference signal configuration section 206 outputsinformation indicating the DMRS mapping pattern.

Demodulation section 203 identifies the positions of DMRSs based on theinformation indicating the DMRS mapping pattern, which is received fromreference signal configuration section 206, then performs channelestimation using the DMRSs and demodulates the data signal.

(Configuration of Base Station 100)

FIG. 9 is a block diagram illustrating a configuration of base station100 according to Embodiment 1. Referring to FIG. 9, base station 100includes reference signal configuration section 101, assignmentinformation generating section 102, error correction coding section 103,modulation section 104, signal assignment section 105, transmissionsection 106, reception section 107, demodulation section 108, and errorcorrection decoding section 109.

Reference signal configuration section 101 generates DMRSs. In addition,reference signal configuration section 101 determines a DMRS mappingpattern for each terminal 200. Specifically, reference signalconfiguration section 101 selects some candidates from all of themapping patterns. In addition, reference signal configuration section101 determines a final DMRS mapping pattern for each subframe.

Reference signal configuration section 101 outputs higher layersignaling indicating the selected mapping pattern candidates to errorcorrection coding section 103 as a control signal. Reference signalconfiguration section 101 also outputs the generated DMRSs andinformation indicating the DMRS mapping pattern selected from thecandidates to signal assignment section 105.

When a downlink data signal (DL data signal) to be transmitted and anuplink data signal (UL data signal) to be assigned to the uplink (UL)are present, assignment information generating section 102 determinesresources (RB pairs) to which the data signal is assigned, and generatesassignment information (DL assignment and UL grant). The DL assignmentincludes information about the DL data signal assignment and informationindicating the DMRS mapping pattern received from reference signalconfiguration section 101. The UL grant includes information about anallocated resource for the UL data signal to be transmitted fromterminal 200. The DL assignment is outputted to signal assignmentsection 105. The UL grant is outputted to signal assignment section 105and reception section 107.

Error correction coding section 103 uses, as input, the transmissiondata signal (DL data signal), and the control signal received fromreference signal configuration section 101, then performs errorcorrection coding on the input signals and outputs the resultant signalto modulation section 104.

Modulation section 104 performs modulation processing on the receivedsignal and outputs the modulated signal to signal assignment section105.

Signal assignment section 105 assigns the assignment information, whichincludes the information indicating the DMRS mapping pattern, and whichis received from assignment information generating section 102 (DLassignment and UL grant), to an EPDCCH or PDCCH. In addition, signalassignment section 105 assigns the data signal received from modulationsection 104 to a downlink resource corresponding to the assignmentinformation (DL assignment) received from assignment informationgenerating section 102. Moreover, signal assignment section 105 assignsthe DMRSs received from reference signal configuration section 101 onthe basis of the information indicating the DMRS mapping pattern, whichis also received from reference signal configuration section 101. Itshould be noted that, signal assignment section 105 assigns a PDSCH(data signal) to an RE corresponding to a reduced DMRS in a PDSCHregion.

As described above, a transmission signal is formed by assignment of theassignment information, DMRSs, and data signal to predeterminedresources. The transmission signal thus formed is outputted totransmission section 106.

Transmission section 106 performs transmission processing such asup-conversion or the like on the received signal and transmits theprocessed signal to terminal 200 via an antenna.

Reception section 107 receives, via an antenna, a signal transmittedfrom terminal 200 and outputs the received signal to demodulationsection 108. Specifically, reception section 107 demultiplexes, from thereceived signal, a signal corresponding to the resources indicated bythe UL grant received from assignment information generating section102, then performs reception processing such as down-conversion on thedemultiplexed signal and outputs the processed signal to demodulationsection 108. Reception section 107 (extracts) receives an A/N signalfrom a signal corresponding to a PUCCH resource associated with an ECCEindex received from signal assignment section 105.

Demodulation section 108 performs demodulation processing on thereceived signal and outputs the processed signal to error correctiondecoding section 109.

Error correction decoding section 109 decodes the received signal toobtain a received data signal from terminal 200.

(Configuration of Terminal 200)

FIG. 10 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1. Referring to FIG. 10, terminal 200 includesreception section 201, signal demultiplexing section 202, demodulationsection 203, error correction decoding section 204, control signalreceiving section 205, reference signal configuration section 206, errorcorrection coding section 207, modulation section 208, signal assignmentsection 209, and transmission section 210.

Reception section 201 receives, via an antenna, a signal transmittedfrom base station 100, then performs reception processing such asdown-conversion on the received signal and outputs the processed signalto signal demultiplexing section 202.

Signal demultiplexing section 202 extracts a control signal for resourceallocation from the received signal, which is received from receptionsection 201, and outputs the control signal to control signal receivingsection 205. In addition, signal demultiplexing section 202 extracts,from the received signal, a signal corresponding to the data resources(i.e., DL data signal) indicated by DL assignment outputted from controlsignal receiving section 205 and outputs the extracted signal todemodulation section 203.

Demodulation section 203 identifies the positions of DMRSs on the basisof the information indicating the DMRS mapping pattern, which isreceived from reference signal configuration section 206, and performschannel estimation using the DMRSs. Demodulation section 203 demodulatesthe signal outputted from signal demultiplexing section 202 on the basisof the channel estimation and outputs the demodulated signal to errorcorrection decoding section 204.

Error correction decoding section 204 decodes the received signal toobtain the received data signal from base station 100. Error correctiondecoding section 204 particularly outputs the control signal indicatingthe DMRS mapping pattern candidates to reference signal configurationsection 206.

Control signal receiving section 205 detects a control signal (DLassignment or UL grant) intended for terminal 200 by blind-decodingsignal components received from signal demultiplexing section 202. Morespecifically, control signal receiving section 205 receives a controlsignal assigned to one of a plurality of assignment candidates forming asearch space configured in reference signal configuration section 206.Control signal receiving section 205 outputs the detected DL assignmentintended for terminal 200 to signal demultiplexing section 202 andoutputs the detected UL grant intended for terminal 200 to signalassignment section 209. Control signal receiving section 205 alsooutputs the information indicating the DMRS mapping pattern, which isincluded in the DL assignment, to reference signal configuration section206.

Reference signal configuration section 206 determines the final DMRSmapping pattern on the basis of the control signal indicating the DMRSmapping pattern candidates outputted from error correction decodingsection 204 and the information indicating the DMRS mapping patterndetermined from the candidates, which is outputted from control signalreceiving section 205. Reference signal configuration section 206outputs the information indicating the determined DMRS mapping patternto demodulation section 203.

Error correction coding section 207 receives the transmission datasignal (UL data signal) as input, then performs error correction codingon the received signal and outputs the processed signal to modulationsection 208.

Modulation section 208 modulates the received signal and outputs themodulated signal to signal assignment section 209.

Signal assignment section 209 assigns the received signal according tothe UL grant received from control signal receiving section 205 andoutputs the resultant signal to transmission section 210.

Transmission section 210 performs transmission processing such asup-conversion on the received signal and transmits the processed signalto base station 100 via an antenna.

As described above, according to Embodiment 1, a DMRS mapping patterncan be configured for each terminal. Thus, it is possible to map DMRSsin a way adapted to the reception environment of each terminal andthereby to minimize the degradation of reception quality due to the DMRSreduction. For example, it is possible to assign a mapping pattern inwhich DMRSs are reduced in the time-domain direction to a low-mobilityterminal, while assigning a mapping pattern in which DMRSs are reducedin the frequency-domain direction to a terminal with small delay spread.Moreover, a data signal can be assigned to the REs corresponding to thereduced DMRSs, which enables communication with a higher transmissionrate.

(Variation of Embodiment 1)

In this variation, when a plurality of RB pairs is allocated, a DMRSmapping pattern is changed according to the RB pair number in order toimprove channel estimation accuracy. In particular, if the same DMRSmapping pattern is used for all of the RB pairs in a case where thenumber of DMRSs assigned to the OFDM symbols in the first slot (OFDMsymbols #5 and #6 in the case of normal CP) is different from the numberof DMRSs assigned to the OFDM symbols in the second slot (OFDM symbols#12 and #13 in the case of normal CP), imbalance in DMRS mapping occursin the time-domain direction. When DMRSs are mapped out of balance,imbalance in DMRS transmission power per OFDM symbol also occurs. Forthis reason, in order to equalize the number of DMRSs on each of theOFDM symbols where DMRSs are mapped, the mapping of the DMRS groups isreversed between the first slot and second slot of an odd-numbered RBpair with respect to the mapping of DMRS groups in an even-numbered RBpair.

FIGS. 11A and 11B and 12A and 12B are diagrams illustrating examples ofDMRS mapping patterns in this variation. FIGS. 11A and 11B illustrate anexample of a bit sequence, ABCDEF=101010, which indicates a case wherethe number of DMRS groups is different between the first slot and secondslot. When no reversal is made between the first slot and second slot(see, FIG. 11A), ABC correspond to the first slot (OFDM symbols #5 and#6) and DEF correspond to the second slot (OFDM symbols #12 and #13) inboth of the even PRB pair and the odd PRB pair. As a result, the numberof DMRSs transmitted on OFDM symbols #5 and #6 is different from thenumber of DMRSs transmitted on OFDM symbols #12 and #13. When themapping of DMRS groups is reversed between the first slot and secondslot of the odd RB pair with respect to the mapping of DMRS groups inthe even RB pair (see, FIG. 11B), ABC correspond to the first slot andDEF correspond to the second slot in the even PRB pair, while ABCcorrespond to the second slot and DEF correspond to the first slot inthe odd-numbered PRB pair. As a result, the number of DMRSs on the OFDMsymbols on which the DMRSs are mapped can be equalized. Thus, the DMRStransmission power on the OFDM symbols on which the DMRSs are mapped canbe equal to each other.

It should be noted that, this variation is applied only to a case wherethe number of DMRS groups is different between the first and secondslots and does not have to be applied to a case where the number of DMRSgroups is the same. FIGS. 12A and 12B illustrate an example of a bitsequence, ABCDEF=001100, which indicates a case where the number of DMRSgroups is the same between the first slot and second slot. When noreversal is made between the first slot and second slot (see, FIG. 12A),the interval between the DMRSs on the same OFDM symbol cannot be greaterthan or equal to 12 subcarriers. However, when reversal is made betweenthe first slot and second slot (see, FIG. 12B), the interval between theDMRSs on the same OFDM symbol may become equal to or greater than 12subcarriers. When the interval in the frequency-domain direction is toolarge, the channel estimation accuracy in the frequency-domain directionis degraded. For this reason, in order to prevent the degradation ofchannel estimation accuracy in the frequency-domain direction, thisvariation is applied only to a case where the number of DMRS groups isdifferent between the first slot and second slot and is not applied to acase where the number of DMRS groups is the same between the first slotand second slot.

(Embodiment 2)

(Summary) In Embodiment 2, hopping which changes the positions of DMRSgroups every subframe is applied with respect to a DMRS mapping pattern.Because of the application of hopping, DMRSs are mapped in mutuallydifferent resources in a plurality of subframes. Each terminal in thiscase can thus perform channel estimation for a PDSCH using a valueobtained by interpolating these DMRSs, which in turn can improve thechannel estimation accuracy.

As a method of hopping, there are random hopping which changes aresource according to a rule different for each terminal on the basis ofthe default value, and cyclic shift hopping which performs cyclicshifting in the time-domain (subframe) direction or in thefrequency-domain (subcarrier) direction on the basis of the defaultvalue.

In random hopping, a different resource is selected in each subframe ona per terminal or cell basis. Accordingly, even when DMRSs areconfigured so as to avoid a collision between DMRSs using defaultvalues, a collision between DMRSs may occur in a different subframe. Forthis reason, random hopping can randomize interference rather thancoordinating interference. Accordingly, random hopping is effective whencoordination between base stations is difficult.

On the other hand, in cyclic shift hopping, DMRSs configured so as toavoid a collision using default values can avoid a collision in the nextsubframe as well. Accordingly, it is possible to coordinate interferenceusing the default values. However, when DMRSs collide with each other inthe configuration using the default values, DMRSs also collide with eachother in the next subframe. For this reason, cyclic shift hopping iseffective when coordination between base stations is easy.

FIG. 13 is a diagram illustrating an example of a DMRS mapping patternaccording to Embodiment 2. FIG. 13 illustrates an example of cyclicshift hopping. The DMRS mapping pattern of this example corresponds to abit sequence, ABCDEF=1000101. In this example, DMRS groups arecyclically shifted in the frequency-domain direction on the same OFDMsymbols in each subframe. Accordingly, shifting of resources isperformed among DMRS groups ABC, while shifting of resources isperformed among DMRS groups DEF. For example, DMRS group A is mapped onsubcarriers #0 and #1 in subframe 0 and is mapped on subcarriers #10 and#11 in subframe #1, while being mapped on subcarriers #5 and #6 insubframe 2.

As described above, when cyclic shift hopping of DMRS groups in thefrequency-domain is applied, the amount of resources used fortransmitting DMRSs on the OFDM symbols on which the DMRSs are mappedremains the same between subframes. Thus, the channel estimationaccuracy in the time-domain can be kept at the same level as that of theinitial mapping of DMRSs.

In addition, when random hopping is applied, it is preferable toconfigure a hopping pattern for each terminal or cell. When a differenthopping pattern is configured for each terminal, a terminal ID (UEID) orC-RNTI can be used for calculating the hopping pattern for eachterminal. Accordingly, each terminal can be configured with a differenthopping pattern. Moreover, when a different hopping pattern isconfigured for each base station, a base station ID (e.g., physical cellID (PCI)) can be used for calculating the hopping pattern for each basestation. Accordingly, each base station can be configured with adifferent hopping pattern.

In addition, as illustrated in FIG. 13, higher layer signaling may beadded for indicating hopping ON/OFF. When hopping is ON, each terminalreceives DMRSs according to a previously specified hopping pattern, andwhen hopping is OFF, each terminal receives DMRSs while assuming that nohopping is applied. Furthermore, higher layer bits may be added asfollows to specify hopping ON/OFF and hopping patterns in a more detailmanner. This addition of higher layer bits improves flexibility.

-   00 hopping off-   01 cyclic shift hopping-   10 UE specific random hopping-   11 Cell specific random hopping

Embodiment 2 is effective when a plurality of subframes is assigned to asingle terminal in particular. Assigning a plurality of subframes to asingle terminal simultaneously is called “multi-subframe assignment.”When a terminal is assigned multi-subframes, the terminal recognizesthat the plurality of subframes is intended for the terminal and thuscan assume that the DMRSs mapped in the plurality of subframescorrespond to the same precoding. Accordingly, the terminal can performchannel estimation using a value obtained by interpolating DMRSs of theadjacent subframes. In this case, when DMRSs are mapped on differentsubcarriers between subframes, the channel estimation accuracy in thefrequency-domain direction can be improved. In this respect, when randomhopping or cyclic shift hopping between subframes is applied, DMRSs aremapped on different subcarriers between the subframes. Thus, the channelestimation accuracy in the frequency-domain direction can be improved.

It should be noted that, although Embodiment 2 has been describedregarding a case where hopping which changes a DMRS mapping patternbetween subframes is applied, the present invention is not limited tothis case, and hopping that changes a DMRS mapping pattern between RBsmay be applied. In particular, when the amount of resources for DMRSsare different between the first slot and second slot, applying hoppingin the time-domain direction can equalize the amount of resources forDMRS by DMRS hopping, which enables equalization of the DMRStransmission power.

(Additional Embodiments)

-   (1) Although a PDSCH is mapped in the REs corresponding to reduced    DMRSs in Embodiments 1 and 2, no PDSCH is mapped in the REs    corresponding to reduced DMRSs. Stated differently, the power for    the DMRSs is set to zero. A DMRS of this kind is called a zero power    DMRS. In particular, additional embodiment (1) provides an advantage    in that even when DMRSs are transmitted using increased transmission    power, there is no increase in the amount of interference to a PDSCH    or DMRS between terminals each configured with a DMRS pattern in    such a way as to avoid overlapping of DMRS mapping between    terminals.

FIGS. 14A and B are diagrams each illustrating an example of a DMRSmapping pattern according to additional embodiment (1). FIG. 14illustrates an example in which zero power DMRSs are applied. In thisexample, one bit is added to higher layer signaling to indicate ON/OFFof zero power DMRS. When zero power DMRS is OFF (see, FIG. 14A), a PDSCHis mapped and transmitted in the REs corresponding to the DMRS groups inwhich no DMRSs are mapped. When zero power DMRS is ON (see, FIG. 14B),no PDSCH is mapped in the REs corresponding to the DMRS groups in whichno DMRSs are mapped.

-   (2) As described above, when a terminal is assigned multi-subframes,    the terminal recognizes that the plurality of subframes is intended    for the terminal and thus can assume that the DMRSs mapped in the    plurality of subframes correspond to the same precoding. However,    since no DMRS in the previous subframe can be used in the first    assigned subframe, the channel estimation accuracy of the top part    OFDM symbols is degraded. For this reason, DMRSs are mapped in both    of the slots in the top sub frame.

FIG. 15 is a diagram illustrating an example of a DMRS mapping patternaccording to additional embodiment (2). The DMRS mapping pattern in FIG.15 corresponds to a bit sequence, ABCDEF=000101, which is a pattern inwhich DMRSs are mapped only in the second slot. In addition, in theexample illustrated in FIG. 15, contiguous subframes 0, 1, and 2 areassigned. In this case, DMRSs are mapped on DMRS groups D and F insubframes 1 and 2 according to the DMRS mapping pattern, and a PDSCH ismapped in the other DMRS resources. Meanwhile, DMRSs are mapped in thefirst slot in subframe 0, which is the first subframe. The mappingpattern in the first slot uses the same subcarriers as those used in thesecond slot. Accordingly, the channel estimation accuracy of the firstassigned subframe can be improved.

In this additional embodiment, the DMRS mapping pattern used in thefirst slot is configured to be identical with those configured in thesecond slot. However, DMRSs may be mapped in all DMRS groups A, B, and Cin the first slot. Accordingly, the same format can be used with anyDMRS mapping pattern.

-   (3) In additional embodiment (3), application of a DMRS mapping    pattern is limited for the purpose of supporting MU-MIMO. When    MU-MIMO is applied, it is easier to remove interference between    DMRSs if the REs in which the DMRSs are mapped are the same between    terminals. Particularly, in multiplexing for antenna port #7 and    antenna port #8 by means of OCCs, since the DMRSs are orthogonally    multiplexed when DMRSs are mapped on the same REs, the terminal can    remove interference between the DMRSs and thus can improve the    channel estimation accuracy. In addition, MU-MIMO is used mainly    using antenna ports #7 and #8. In LTE-Advanced, whether or not    MU-MIMO is applied is not indicated to terminals. Accordingly, each    terminal receives signals intended for the terminal without knowing    whether or not MU-MIMO is applied.

In this respect, in additional embodiment (3), a base station isconfigured to map, when antenna ports #7 and #8 are assigned, butantenna port #9 is not assigned, DMRSs on all DMRS groups (allDMRS-mappable REs) (see, FIG. 16A) or to map DMRSs according to apredetermined DMRS mapping pattern (see, FIG. 16B) even in a DMRSmapping pattern in which DMRSs are reduced. Accordingly, the same DMRSmapping pattern is used between terminals forming a pair in MU-MIMO, andinterference between DMRSs can be removed in each terminal. Thepredetermined DMRS mapping pattern used in this case may be a patterncommon to all the terminals, or may be a different pattern configuredfor each terminal according to the UE-ID or the like of the terminal.When the predetermined DMRS mapping pattern is different betweenterminals, for transmission of DMRSs in the same REs, the base stationselects terminals assigned the same DMRS mapping pattern, as an MU-MIMOpair.

As described above, terminals cannot determine whether or not MU-MIMO isapplied, because of the assignment of antenna ports #7 and #8, but theterminals can configure the same DMRS assignment resources by changing aDMRS mapping pattern, when MU-MIMO is applied.

-   (4) In additional embodiment (4), a base station may indicate the    intervals (in frequency-domain or time-domain direction) between    DMRS groups in which DMRSs are mapped to a terminal.

In this case, the terminal determines the transmission positions ofDMRSs over a plurality of RB pairs according to the intervals.

FIGS. 17A, B, and C are diagrams illustrating examples of DMRS mappingpatterns according to additional embodiment (4). FIGS. 17A, B, and Cillustrate examples when the intervals in the frequency-domain directionare indicated. FIG. 17A illustrates an example in which DMRSs are mappedaccording to the current mapping pattern. FIG. 17B illustrates anexample in which DMRSs are mapped in every other DMRS group in thefrequency-domain direction using the current mapping pattern as thebasis. FIG. 17C is an example in which DMRSs are mapped in every thirdDMRS group in the frequency-domain direction using the current mappingpattern as the basis. In the current mapping of DMRS groups, some DMRSgroups are mapped at the boundary between RB pairs in thefrequency-domain. Since these DMRS groups are mapped adjacent to eachother, the channel estimation accuracy for the resources near the DMRSsgroups is excessively high. In FIG. 17B, since DMRSs are transmittedonly in one of the two adjacent DMRS groups, the number of DMRSs can bereduced while the degradation of channel estimation accuracy in thefrequency-domain direction is minimized. It should be noted that, inthis embodiment, the number of indicating bits can be reduced ascompared with the case where the presence or absence of DMRStransmission in six DMRS groups is indicated, individually.

-   (5) In the present invention, the elements of each DMRS group may be    mapped in a different order. Hereinafter, a description will be    provided regarding an example of a case where the elements of each    DMRS group are “abcd.” Elements abcd of length-4 OCC are expressed    by the following equation.

$\begin{matrix}{W_{4} = {\begin{pmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{pmatrix} = \begin{pmatrix}a & b & c & d\end{pmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

As illustrated in FIG. 18A, abcd is mapped in such a way that adifferent element is allocated to each antenna port, and for antennaports #7, #8, #11, and #13, the elements in ascending order abcd (“→” inthe drawings) and the elements in descending order dcba (“←” in thedrawings), which is reversal of the ascending order, are alternatelymapped in the frequency-domain. In this manner, transmission of the samephase signals on the OFDM symbols is prevented. Likewise, for antennaports #9, #10, #12, and #14, the elements in the order, cdab (“→*” inthe drawings), and the elements in the order reversal to the order, badc(“←” in the drawings) are alternately mapped. However, when every otherDMRS group is mapped in the frequency-domain direction (see, FIG. 18B),only the OCC sequences of the same order (“<←” in the drawings) areselected, which in turn deteriorates the power balance. For this reason,as illustrated in FIG. 18C, it is possible to define that the ascendingorder and descending order are alternately used in DMRS groups to betransmitted.

[Others]

-   [1] In the present invention, a DMRS mapping pattern is not applied    to an EPDCCH transmitted in a PDSCH region. Mapping of an EPDCCH is    defined in such a way as to avoid an RE on which a DMRS is mapped.    In addition, an RE on which an EPDCCH is mapped is shared by a    plurality of terminals. For this reason, when a different mapping    pattern is configured for each terminal, it becomes difficult to map    an EPDCCH on the same RB.-   [2] In the present invention, a DMRS mapping pattern may be applied    to an EPDCCH transmitted in a PDSCH region. In this case, the DMRS    mapping pattern may be indicated by higher layers when an EPDCCH set    is assigned. In this manner, the code rate of EPDCCH can be reduced,    and the resource usage efficiency can be improved when the channel    quality is good.-   [3] In the present invention, the application of a DMRS mapping    pattern may be limited in such a way that a DMRS mapping pattern is    applied only when a scheme with a larger M-ary modulation number    (such as 16QAM, 64QAM, or 256QAM) or a scheme with a higher coding    rate is used. DMRS reduction is effective when the channel quality    is good. When the channel quality is good, a scheme with a larger    M-ary modulation number is used. Likewise, a when the channel    quality is good, a scheme using a higher coding rate is used.

Accordingly, the application of a DMRS mapping pattern may be limited insuch a way that a DMRS mapping pattern is applied only when a schemewith a larger M-ary modulation number or a scheme using a higher codingrate is used. With this configuration, since a mapping pattern in whichno DMRS is reduced is used when the channel quality is poor, the DMRSreception quality can be secured. In LTE, these m-ary number and codingrate are determined according to the modulation and coding scheme (MCS)table. Thus, whether or not to apply a DMRS mapping pattern may bedetermined according to the index of the MCS table.

-   [4] In Embodiment 1, the unit of DMRSs indicated by a single bit    (i.e., DMRS group) is defined as a group of four REs corresponding    to two adjacent REs in the subcarrier direction and two adjacent REs    in the OFDM symbol direction when the number of antenna ports is at    least three (i.e., when antenna port #9 is used). However, the    present invention is by no means limited to this case, and the unit    of DMRSs may be defined as two adjacent OFDM symbols. In this case,    the number of bits required for indicating is 12 bits. With this    configuration, the number of DMRSs to be reduced can be configured    separately between antenna ports #7, #8, #11, and #13, and antenna    ports #9, #10, #12, and #14. For example, when antenna ports #7 to    #10 are used in a certain cell while antenna ports #7 and #8 are    used in another cell, the number of resources to be used by the cell    can be reduced in order to reduce interference to the DMRSs of the    other cell.-   [5] In the present invention, a base station may indicate DMRS    groups in a plurality of RBs to a terminal, simultaneously. For    example, when there are six DMRS groups per RB pair, 12 DMRS groups    are simultaneously indicated using 12 bits for two RB pairs, and 18    DMRS groups are simultaneously indicated using 18 bits for three RB    pairs, and the pattern is repeated every two RB pairs, or every    three RB pairs. Specifically, when an assignment with a small number    of DMRS groups is selected, a pattern which is well balanced in the    time-domain and frequency-domain directions can be selected.-   [6] The term “antenna port” refers to a logical antenna including    one or more physical antennas. In other words, the term “antenna    port” does not necessarily refer to a single physical antenna, and    may sometimes refer to an antenna array including a plurality of    antennas, and/or the like.

For example, 3GPP LTE does not specify the number of physical antennasforming an antenna port, but specifies an antenna port as a minimum unitallowing a base station to transmit a different reference signal.

In addition, an antenna port may be specified as a minimum unit formultiplication of a precoding vector weighting.

-   [7] The above-noted embodiments have been described by examples of    hardware implementations, but the present invention can be also    implemented by software in conjunction with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

A transmission apparatus according to an aspect of the embodimentsincludes: a reference signal configuration section that configures ademodulation reference signal (DMRS) mapping pattern for each receptionapparatus; and a transmission section that transmits a transmissionsignal including information indicating the DMRS mapping pattern, and aDMRS mapped in a resource according to the DMRS mapping pattern.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection configures the DMRS mapping pattern for each subframe.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection configures the DMRS mapping pattern by determining whether ornot to map the DMRS in each DMRS group including a plurality of adjacentresource units in which the DMRS is mappable.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection configures the DMRS mapping pattern by previously indicatingcandidates for the DMRS mapping pattern to each reception apparatus viahigher layer signaling, and thereafter dynamically selecting one of thecandidates for the DMRS mapping pattern.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection configures the DMRS mapping pattern for each enhanced physicaldownlink control channel (EPDCCH) set or PDCCH set via higher layersignaling.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection configures the DMRS mapping pattern for each EPDCCH candidateposition via higher layer signaling.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection selects the DMRS mapping pattern according to the number ofallocated RB pairs.

The transmission apparatus according to an aspect of the embodimentemploys a configuration in which the reference signal configurationsection selects the DMRS mapping pattern according to a systembandwidth.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection selects the DMRS mapping pattern according to the number ofallocated contiguous RB pairs.

The transmission apparatus according to an aspect of the embodimentemploys a configuration in which the reference signal configurationsection selects the DMRS mapping pattern according to an allocated RBpair number or resource block group (RBG) number.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which: the DMRS mapping pattern includes theDMRS group in both of a first slot formed including a first-half RB ofthe PRB pair and a second slot including a second-half RB of the PRBpair; and the reference signal configuration section reverses mapping ofthe DMRS group between the first slot and second slot of one of anodd-numbered RB pair and an even-numbered RB pair with respect tomapping of the DMRS group between the first slot and second slot of theother one of the odd-numbered RB pair and the even-numbered RB pair.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the information indicating the DMRSmapping pattern is a bit sequence that indicates, using a single bit,whether or not to map the DMRS in each of the DMRS groups.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which a first bit sequence that indicates notto map the DMRS in any of the DMRS groups indicates a differentoperation.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the first bit sequence indicates to mapthe DMRS on top two OFDM symbols.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the first bit sequence indicates to mapthe DMRS in every other resource block (RB) pair.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the first bit sequence indicates todemodulate a physical downlink shared channel (PDSCH) using a cellspecific reference signal (CRS).

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection changes a position of the DMRS group for each subframe.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection changes a position of the DMRS group between RBs.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection assigns a PDSCH to a resource unit of a DMRS group in which theDMRS is not mapped.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection sets transmission power of a resource unit of a DMRS group inwhich the DMRS is not mapped to zero.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which: the DMRS mapping pattern includes theDMRS group in both of a first slot including a first-half RB of a PRBpair and a second-half of the PRB pair; and when selecting a DMRSmapping pattern in which the DMRS is mapped only in the DMRS group inthe second slot and also assigning a plurality of subframes to apredetermined reception apparatus, the reference signal configurationsection maps the DMRS in the DMRS group in the first slot of a top subframe.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which, when antenna ports #7 and #8 areassigned but antenna port #9 is not assigned, the reference signalconfiguration section maps a DMRS in all DMRS groups, or maps a DMRSaccording to a predetermined DMRS mapping pattern.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the transmission section includesinformation in the transmission signal, the information indicating aninterval in a frequency-domain direction or a time-domain directionbetween DMRS groups in which the DMRS is to be mapped.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection configures resource units of each of the DMRS groups to bemapped in a different order.

The transmission apparatus according to an aspect of the embodimentsemploys a configuration in which the reference signal configurationsection alternately uses an ascending order and a descending order formapping of the resource units of the DMRS groups in which the DMRS is tobe mapped.

A reception apparatus according to an aspect of the embodimentsincludes: a reference signal configuration section that configures aDMRS mapping pattern based on a control signal included in a receivedsignal; and a demodulation section that identifies a position of a DMRSbased on the DMRS mapping pattern, then performs channel estimationusing the DMRS, and demodulates a data signal.

A control signal mapping method according to an aspect of theembodiments includes: configuring a demodulation reference signal (DMRS)mapping pattern for each reception apparatus; and transmitting atransmission signal including information indicating the DMRS mappingpattern and a DMRS mapped in a resource according to the DMRS mappingpattern.

A demodulation method according to an aspect of the embodimentsincludes: configuring a DMRS mapping pattern based on a control signalincluded in a received signal; identifying a position of a DMRS based onthe DMRS mapping pattern; performing channel estimation using the DMRS;and demodulating a data signal.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in mobile communicationsystems compliant with LTE-Advanced.

REFERENCE SIGNS LIST

-   100 Base station-   200 Terminal-   101, 206 Reference signal configuration section-   102 Assignment information generating section-   103, 207 Error correction coding section-   104, 208 Modulation section-   105, 209 Signal assignment section-   106, 210 Transmission section-   107, 201 Reception section-   108, 203 Modulation section-   109, 204 Error correction decoding section-   202 Signal demultiplexing section-   205 Control signal receiving section

The invention claimed is:
 1. A transmission apparatus comprising:reference signal configuration circuitry, which in operation, configuresa demodulation reference signal (DMRS) mapping pattern for eachreception apparatus by determining whether or not to map a DMRS in eachof a plurality of DMRS groups including a plurality of adjacent resourceunits in which the DMRS is mappable; and a transmitter that transmits atransmission signal including information indicating the DMRS mappingpattern, and the DMRS mapped in a resource according to the DMRS mappingpattern.
 2. The transmission apparatus according to claim 1, wherein thereference signal configuration circuitry, in operation, configures theDMRS mapping pattern for each subframe.
 3. The transmission apparatusaccording to claim 1, wherein the reference signal configurationcircuitry, in operation, configures the DMRS mapping pattern bypreviously indicating candidates for the DMRS mapping pattern to eachreception apparatus via higher layer signaling, and thereafterdynamically selecting one of the candidates for the DMRS mappingpattern.
 4. The transmission apparatus according to claim 1, wherein thereference signal configuration circuitry, in operation, configures theDMRS mapping pattern for each enhanced physical downlink control channel(EPDCCH) set or physical downlink control channel (PDCCH) set via higherlayer signaling.
 5. The transmission apparatus according to claim 1,wherein the reference signal configuration circuitry, in operation,configures the DMRS mapping pattern for each enhanced physical downlinkcontrol channel (EPDCCH) candidate position via higher layer signaling.6. The transmission apparatus according to claim 1, wherein thereference signal configuration circuitry, in operation, selects the DMRSmapping pattern according to a number of allocated resource block (RB)pairs.
 7. The transmission apparatus according to claim 1, wherein thereference signal configuration circuitry, in operation, selects the DMRSmapping pattern according to a system bandwidth.
 8. The transmissionapparatus according to claim 1, wherein the reference signalconfiguration circuitry, in operation, selects the DMRS mapping patternaccording to a number of allocated contiguous resource block (RB) pairs.9. The transmission apparatus according to claim 1, wherein thereference signal configuration circuitry, in operation, selects the DMRSmapping pattern according to an allocated resource block (RB) pairnumber or resource block group (RBG) number.
 10. The transmissionapparatus according to claim 9, wherein: the DMRS mapping patternincludes a DMRS group in both of a first slot formed including afirst-half RB of a physical resource block (PRB) pair and a second slotincluding a second-half RB of the PRB pair; and the reference signalconfiguration circuitry, in operation, reverses mapping of the DMRSgroup between the first slot and second slot of one of an odd-numberedRB pair and an even-numbered RB pair with respect to mapping of the DMRSgroup between the first slot and second slot of the other one of theodd-numbered RB pair and the even-numbered RB pair.
 11. The transmissionapparatus according to claim 1, wherein the information indicating theDMRS mapping pattern is a bit sequence that indicates, using a singlebit, whether or not to map the DMRS in each of the DMRS groups.
 12. Thetransmission apparatus according to claim 11, wherein a first bitsequence that indicates not to map the DMRS in any of the DMRS groupsindicates a different operation.
 13. The transmission apparatusaccording to claim 12, wherein the first bit sequence indicates to mapthe DMRS on top two orthogonal frequency division multiplexing (OFDM)symbols.
 14. The transmission apparatus according to claim 12, whereinthe first bit sequence indicates to map the DMRS in every other resourceblock (RB) pair.
 15. The transmission apparatus according to claim 12,wherein the first bit sequence indicates to demodulate a physicaldownlink shared channel (PDSCH) using a cell specific reference signal(CRS).
 16. The transmission apparatus according to claim 1, wherein thereference signal configuration circuitry, in operation, changes aposition of a DMRS group for each subframe.
 17. The transmissionapparatus according to claim 1, wherein the reference signalconfiguration circuit, in operation, changes a position of a DMRS groupbetween resource blocks (RBs).
 18. The transmission apparatus accordingto claim 1, wherein the reference signal configuration circuitry, inoperation, assigns a physical downlink shared channel (PDSCH) to aresource unit of a DMRS group in which the DMRS is not mapped.
 19. Thetransmission apparatus according to claim 1, wherein the referencesignal configuration circuitry, in operation, sets transmission power ofa resource unit of a DMRS group in which the DMRS is not mapped to zero.20. The transmission apparatus according to claim 1, wherein: the DMRSmapping pattern includes a DMRS group in both of a first slot includinga first-half resource block (RB) physical resource block (PRB) pair anda second-half of the PRB pair; and when selecting a DMRS mapping patternin which the DMRS is mapped only in the DMRS group in the second slotand also assigning a plurality of subframes to a predetermined receptionapparatus, the reference signal configuration circuitry, in operation,maps the DMRS in the DMRS group in the first slot of a top subframe. 21.The transmission apparatus according to claim 1, wherein, when antennaports #7 and #8 are assigned but antenna port #9 is not assigned, thereference signal configuration circuitry, in operation, maps a DMRS inall DMRS groups, or maps a DMRS according to a predetermined DMRSmapping pattern.
 22. The transmission apparatus according to claim 1,wherein the transmitter includes information in the transmission signal,the information indicating an interval in a frequency-domain directionor a time-domain direction between the DMRS groups in which the DMRS isto be mapped.
 23. The transmission apparatus according to claim 1,wherein the reference signal configuration circuitry, in operation,configures resource units of each of the DMRS groups to be mapped in adifferent order.
 24. The transmission apparatus according to claim 23,wherein the reference signal configuration circuitry, in operation,alternately uses an ascending order and a descending order for mappingof the resource units of the DMRS groups in which the DMRS is to bemapped.
 25. A control signal mapping method comprising: configuring ademodulation reference signal (DMRS) mapping pattern for each receptionapparatus by determining whether or not to map a DMRS in each of aplurality of DMRS groups including a plurality of adjacent resourceunits in which the DMRS is mappable; and transmitting a transmissionsignal including information indicating the DMRS mapping pattern and theDMRS mapped in a resource according to the DMRS mapping pattern.